Developmental changes in the ability to synthesize juvenile hormone in vitro by corpora allata from the Eri silkworm, Samia cynthia ricini (Lepidoptera: Saturniidae)

Abstract

Abstract. A radiochemical assay (RCA) has been used for the measurement ofjuvenile hormone (JH) synthesis in vitro by corpora allata (CA) from the Eri silkworm, Samia cynthia ricini. Using CA from newly emerged female adults for the bioassay, the most suitable incubation conditions were determined. A high rate of JH synthesis was found in medium TC199 at pH 6.5, 30°C and 4 mM Ca2+. The time course of JH synthesis showed a steady decrease during the first 6 hours of incubation.Under optimal incubation conditions, CA from the 4th and 5th larval instars, pupae and adults were used for measuring JH syn thesis in vitro. The highest rates of JH synthesis were found on the 1st day of both larval stages, and then JH synthesis decreased steadily during the following two days of each instar. From the 4th day of the 5th larval instar to the 2nd day after pupation, CA could still synthesize small amounts of JH. However, from the 3rd day of the pupal stage to 12 hours before adult emergence, no JH release was observed. About 6 hours before emergence, CA of both female and male pharate adults regained the ability to synthe size JH. JH synthesis increased to a maximum shortly after emergence and then decreased again during the following two days. During this period, JH synthesis in vitro by CA from females was always higher than that of males. This is the first report on JH syn thesis in vitro by CA from both female and male pharate adults and adults of a lepidopteran species, where the adults do not feed, are relatively short-lived, mate only once, and ovarian maturation and vitellogenesis are completed before emergence.

Juvenile hormone acid methyl transferase is a key regulatory enzyme for juvenile hormone synthesis in the Eri silkworm, Samia cynthica ricini

“…Under optimal incubation conditions, two peaks of JH synthesis were found on day 1 of the fifth-instar larvae and at the time of adult emergence. A significant sexual dimorphism of JH synthesis was observed during the period of adult emergence (Li et al, 2002a). This study has demonstrated that Samcri-JHAMT, but not -HMGR, is the key regulatory enzyme for JH synthesis in the Eri silkworm, at both molecular and enzymatic levels.…”

“…Second, JHAMT was regulated at the transcriptional level. During the period of adult emergence, the acute change of Samcri-JHAMT activity exactly matched that of JH synthesis (Li et al 2002a). Although Samcri-JHAMT mRNA level shared a similar pattern to that of Samcri-JHAMT activity, the former peak was a few hours earlier than the later one suggesting a short delay of translational and/or posttranslational processes.…”

“…Samcri-HMGR and -JHAMT mRNA levels in CA on day 1 were 2-and 30-fold higher than those on day 5, respectively. Samcri-JHAMT but not -HMGR mRNA level was paralleled JH synthesis at the larval stages (Li et al, 2002a).…”

“…It is important to note that JHAMT mRNA level and enzyme activity in female CA of S. cynthia ricini were at least 10-fold higher than that of B. mori. The above data should explain the reason why JH synthesis by male CA of B. mori was not detectable (Li et al, 2002a;Kinjoh et al, 2007).…”

Biochemical and molecular characterization of allatotropin and allatostatin from the Eri silkworm, Samia cynthia ricini

“…In Samia cynthia ricini, developmental changes in the CA ability to synthesize JH was investigated in vitro using a modified radiochemical assay (RCA) (Li et al, 2002a). Both AT and AST activities were detected in the brain extracts, and Manse-AT and -AST were shown to stimulate and inhibit, respectively, JH synthesis in isolated CA (Li et al, 2002b).…”